The best way to
determine suitability for discontinuation of mechanical ventilation is to
perform a spontaneous breathing trial. There are three ways to
do this: putting the patient on a minimum pressure support and PEEP
(for example 5-7cmH2O PS/5cmH2O PEEP performing mechanics and extubating),
using CPAP alone, or using a T-piece.

A
T-piece (or trach-collar) trial involves the patient breathing through a
T-piece (essentially the endotracheal tube (ett) plus a flow of oxygen-air
and no ventilatory assistance) for a set period of time. The work of
breathing is higher than through a normal airway (although this simulates
laryngeal edema/airway narrowing). If tolerated, the chances of successful
extubation are high. If not reattachment to a ventilator is simple.
An alternative variant to this is the use of a CPAP circuit, which
overcomes some of the work of breathing through the ett and prevents
airway collapse.
Many physicians extubate the patient directly from PS and PEEP (the PS
overcomes the tube resistance). The conventional wisdom is that 7cmH2O
of pressure support is required to overcome the resistance through a size
7.5mm (internal diameter) endotracheal tube, and 3cmH2O through
a tracheostomy. If a smaller tube is in place, pressure support of 10cmH2O
is required.

If
the patient tolerates a spontaneous breathing trial with any of these
modes, then one should proceed to extubation.

Conduct wean to extubation (spontaneous
breathing) trials early
in the morning, when the patient is fully rested and there is a full
compliment of staff available.

During these trials the patient should
be awake and co-operative, apyrexial and on minimal pressor support
(vasopressors are not a contraindication to extubation, although they
are a sign that the patient may still require pulmonary support).

Place the patient in the upright or
semi-upright position and explain what you are attempting to do.

Check for a cuff leak by deflating the
cuff and occluding the ett. The absence of a cuff leak is not a
contraindication to extubation, as the tube may be snug with the
trachea, but should alert the physician to the possibility of laryngeal
edema.

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